A honeycomb structure made of ceramics has been used for capturing dust and other particulate substances contained in automotive exhaust gas and incineration exhaust gas which occurs at the time of incinerating waste, and furthermore for adsorbing or absorbing the NOx, CO and HC, etc., contained in such exhaust gas. Above all, in such honeycomb structures, cordierite honeycomb structures are used because they have excellent thermal shock resistance (refer to Patent Documents 1 and 2, for example).
A method for producing such a cordierite-type honeycomb structure, for example, that includes extrusion forming a green body, which has increased plasticity, by kneading a ceramic starting material (a forming formulation), water, an organic binder and so on, drying and firing, is disclosed (refer to Patent Document 3, for example). The reason why the organic binders are contained in the green body is that it is difficult to obtain sufficient plasticity and form maintainability using only ceramic material powder and water, therefore. the organic binders and so on are contained in the green body to increase the formability.    Patent Document 1: Japanese Patent Application Laid-open 11-92214    Patent Document 2: Japanese Patent Application Laid-open 11-100259    Patent Document 3: Japanese Patent No. 3227039
The formability of the cordierite type honeycomb structure improves according to the amount of the organic binder added, which gives plasticity and form maintainability. However, if a large amount of organic binder is added, the spaces which are occupied by the organic binder at the time of forming may become defects, because the organic binder will be burnt out at the time of firing. Therefore, there is a problem in that the number of the defects in the honeycomb structure is increased according to the amount of the organic binder added, and this may lead to a decrease in the mechanical strength of the honeycomb structure. Furthermore, in the case of large size honeycomb structures, when the organic binders burn at the time of firing, high thermal stress is occurred by the temperature difference between the inner and the outer of the honeycomb structure because the temperature of the inner part of the honeycomb structure is to be higher than that of the outer part of the honeycomb structure, and this may lead to the occurrence of many defects, such as cracks. By this, there is a problem in that not only is the mechanical strength decreased, but also the productivity or yield is decreased greatly. Furthermore, there also are serious environmental problems such as air pollution, global warming or the like, because of the release of CO2 or poison gases, which are produced by burning the organic binder at the time of firing, into the atmospheric air.
The present invention is made in reference to the above mentioned problems, and is characterized by providing a method for producing a well-shaped honeycomb structure, even though an organic substance, particularly organic binders, are present in the green body in a low amount, and by providing a honeycomb structure obtained by the method for producing the same.